By 1000 BCE urban civilizations of the Eastern Hemisphere were no longer confined to a few irrigated river plains. World population was growing, interregional trade networks were expanding, and towns and cities were appearing where only farming villages or nomad camps had existed before. Iron-making technology had increasing impact on economy and society. Contacts among diverse societies of Eurasia and Africa were intensifying, and these had profound consequences in the period from 1000 BCE to 300 CE. The pace of change was quickening in the Americas as well. If we stand back far enough to take in the global scene, three large-scale patterns of change stand out.